1. Field of the Invention
This invention related to deposition apparatus, and particularly to apparatus for the deposition of films by a low-pressure chemical vapour deposition (LPCVD) process.
2. Description of Related Arts
It is known, for example, to deposit polysilicon films on substrates by supporting the substrates within a deposition chamber, heating the chamber to a temperature of, say 630.degree. C., and maintaining the pressure in the chamber at a very low level, say 10 to 30 Pascals, while passing silane gas through the chamber.
The need to achieve such a very low pressure level presents a problem. A high-capacity pump, such as a turbo-molecular pump, is required, but merely to substitute a high-speed pump in place of a normal pump connected to a LPCVD deposition chamber is found to produce poor uniformity of the films deposited on the substrate.